Alternate Day Fasting: Everything A Newbie Needs to Know

Written and Medically Reviewed by Dr Babar Shahzad, BSc and MBBS on January 21, 2020.

Alternate day fasting (ADF, for short) is one of many ways to practice intermittent fasting (IF). Other IF approaches include the 5:2 diet, 12-hours fasts, 16-hour fasts, 20-hours fasts, and 24-hour fasts.

Whether you are looking for a powerful way to shed some pounds or simply improve your general health, alternate day fasting is just what you need. A growing body of evidence suggests that alternate-day fasting not only helps with weight loss but also promotes heart health and protects from developing diabetes and high blood pressure in both normal weight and overweight individuals. That said, it also comes with some risks that you should not ignore.

Thus, it is critically important to learn the benefits and drawbacks of this method of fasting, especially if you have just started to fast. Doing so will help maximize the results and cut down the chances of potential complications. Keep reading to learn what is alternate day fasting, science-backed benefits and risks, and the foods/drinks to include during fast days.

What is Alternate Day Fasting? Learn the Basics

Alternate day fasting is a time-restricted eating method in which you fast one day and eat normally the next day. Simply put, you have alternating “fasting days” and “feeding days”.

On the fasting days, you may consume no calories or about 500 calories, which contributes to approximately one-fourth of your daily calorie needs. Click here to find out your daily calorie needs based on your age, weight, gender, and activity level.

On the feed days, you can stick to your normal eating habits and consume the foods/drinks you want.

Top 5 Science-Backed Alternate Day Fasting Benefits

Mounting scientific evidence supports the role of alternate day fasting in weight reduction, decreased risk of heart disease, and improved blood glucose and fat levels.

Interestingly, one case report even goes as far as to say that planned intermittent fasting including ADF may help reverse type II diabetes. While it might be too early to jump to a conclusion regarding diabetes reversal, scientists are sure of ADF’s incredible health benefits.

These include:

1. Alternate Day Fasting for Weight Loss

ADF is a powerful weight tool. It is easy to follow. Besides, it has shown promising results in numerous studies.

Obesity has grown into a global epidemic in the last few decades it is one of the major risk factors behind common morbidities such as diabetes, hypertension and heart problems. The World Health Organization (WHO) states that worldwide obesity has nearly tripled since 1975. If you are struggling with weight issues, you should seriously consider ADF. We explain why.

A 2013 study published in Nutrition Journal found that following ADF for 12 weeks caused a loss of nearly 8 lbs of fat mass. Interestingly, another recent study noted that people aged 50-59 years achieved greater weight loss with ADF compared to people of other age groups.

Want to supercharge your weight loss? Consider combining ADF with endurance exercise, suggests a 2013 study published in the journal Obesity. The combination burns at least twice as much fat as an individual approach.

2. Improved Heart Health

Heart disease is the leading cause of death globally. Estimates suggest that diseases of the heart and blood vessels accounted for more than one-third of deaths globally in 2016.

Alternate day fasting helps reduce the risk of heart disease in many ways which would be more fruitful when combined with healthy lifestyle i.e. sound sleep and avoid smoking. It:

3. Better Blood Sugar Control

High blood sugar levels occur when the body fails to produce enough insulin, or cannot properly use available insulin (insulin resistance). In any case, persistently high sugar levels can lead to diabetes.

Studies have shown that short-term alternate day fasting or other forms of intermittent fasting can help reduce fasting blood glucose levels which is abnormally high in diabetic patients. ADF works by reducing the blood levels of insulin and increasing insulin sensitivity.

4. Alternate Day Fasting Promotes Autophagy

Both long-term and short-term fasting is known to trigger autophagy in the body.

Autophagy is a destructive process that recycles unused, damaged, and potentially harmful cell components. In simple terms, “auto” means “itself” and “phagy” means “eating” so when the body's nutrients are not coming from outside, it starts getting them by eating self which is good for overweight people but can cause malnutrition in normal. Autophagy is the body’s way of clearing unwanted substances from the cells.

Autophagy is thought to reduce the risk of many diseases. These include infections, heart disease, obesity, and cancer (but can be harmful in patients already having cancer).

5. Alternate Day Fasting May Be the Fountain of Youth

Restricting total calorie intake, which can be achieved from alternate day fasting, has been shown to significantly prolong lifespan in animal studies.

In many studies, animals that received all necessary nutrients but fewer calories lived longer than their counterparts that received more calories. In fact, the calorie-restricted animals have significantly lower risks of many age-related disorders including cancer.

One study noted that lifelong alternate fasting increased lifespan in male mice primarily by delaying cancer occurrence.

That said, you should interpret these results with caution, as there are currently no studies involving humans and animals results cannot be accurately translated to humans.

Is Alternate Day Fasting Safe? Know the Potential Risks

Alternate day fasting is safe for most people, especially when they practice it for a short period. The long-term negative health effects of alternate day fasting have not been well documented.

However, as with other types of fasting, it may cause problems in people who have chronic illnesses like high blood pressure and diabetes. If you take medications for any of these conditions, you should first consult a health professional before starting any type of fasting. Diabetic people should also know that insulin therapy itself can cause weight gain as one of its major side effects.

Likewise, pregnant and breastfeeding women, children, and those who are underweight should fast only after their doctor gives the green light.

There have been concerns about the effects of ADF on people who have pre-existing eating disorders. However, studies show that such effects are rare and unlikely to cause any long-term issues.

In fact, one study suggests that ADF may actually benefit people with eating disorders.

During the early days of ADF, you may experience:

  • Constipation
  • Dizziness
  • General weakness
  • Bad breath
  • Sleep problems
  • Disturbed menstrual cycles in women
  • Low mood, anxiety and depressive symptoms in normal-weight individuals

Luckily, these problems are mild and usually clear on their own once your body adapts to the new eating habit.

Alternate Day Fasting vs Intermittent Fasting

First thing first, alternate day fasting is a form of intermittent fasting. Both have incredible benefits in promoting weight loss and improving health.

When you google “ADF Vs IF”, you will find hundreds of thousands of results showing different terms like time-restricted eating, the 16/8 Method, the 5:2 Diet, Eat-Stop-Eat, The Warrior Diet and Spontaneous Meal Skipping.

Basically, all these methods are different intermittent fasting approaches.

What you should understand is that your individual response to a certain method may not be the same as that of your friend as basal metabolic rate differs from person to person and each person has different tendencies of losing weight. Simply put, you may benefit from alternate day fasting while your friend may lose pounds with the 16/8 method.

When all is said and done, you should keep in mind that alternate-day fasting is not the best method for a newbie. It is an extreme form of intermittent fasting and you will likely be not able to continue it for longer durations.

Thus, it is important to find the best method of intermittent fasting that addresses your unique individual needs. For this, you will need an expert team that carefully studies your unique physical parameters and designs an intermittent fasting diet protocol to give you the best possible outcome.

Eating/Drinking During the Fasting Days

During the fasting days, you may consume up to 500 calories. To achieve this goal, you should take care of what you eat and drink.

If you are planning for a zero-calorie fast day, make sure to drink plenty of water, unsweetened and creamless tea or coffee only. This is critical to prevent dehydration and hunger pangs.

For a 500-calorie fasting day (which is a part of modified alternate-day fasting), you should take high-protein, low-calorie foods such as lean meat, eggs, and veggies. Warm soups are perfect for fast days as they are gentle on your gut and provide essential nutrition.

Depending on your preference, you may eat a “big” meal once a day or 2-3 small meals throughout the day. The only thing you should not miss is not to consume more than 500 calories.

Below are a few examples of meals you should consider eating on fast days.

  • Eggs
  • Lean Meat
  • Veggies
  • Greek yogurt with berries
  • Soup with a piece of fruit

The Bottom Line

Alternate day fasting is an effective weight-loss tool. Besides, several studies have found that short-term ADF can help improve your general health. It reduces the risk of heart disease and improves glucose metabolism.

ADF has an excellent safety profile and is safe for most people. For an otherwise healthy person, it is quite unlikely to cause any significant health problems. Both normal-weight and overweight (or obese) people can benefit from alternate-day fasting.

Pregnant or lactating women, underweight individuals, and children should consult their doctor before starting any fasting program. If you take medications for high blood pressure or diabetes, start fasting only after talking to your doctor.

For optimal results, it is advisable to consult experts who can help you design specific intermittent fasting diet plans.